To locate and precisely detect disease markers has already been the important precondition for the diagnosis and treatment of various clinical diseases including various tumors; various acute/chronic infectious diseases, e.g. viral diseases such as viral influenza, viral hepatitis, AIDS, SARS, bacterial diseases such as tuberculosis, bacterial pneumonia, and other acute/chronic infectious diseases caused by various pathogenic microorganisms; other acute/chronic diseases such as diseases of respiratory system, diseases of immune system, diseases of blood and hematopoietic system, diseases of circulatory system such as cardio-cerebrovascular diseases, metabolic diseases of endocrine system, diseases of digestive system, diseases of nervous system, diseases of urinary system, diseases of reproductive system and diseases of locomotor system. Although more and more disease markers have been found and utilized in general survey and diagnosis of clinical diseases as well as monitoring and controlling of therapeutic effects, their clinical application effects are obviously insufficient. For instance, tumor marker, e.g. alphafetoprotein, lactic dehydrogenase and carcinoembryonic antigen have been widely used in clinic. But these disease markers are far from meeting the needs of early diagnosis for cancer for the following two main reasons: (1) the sensitivity and specificity for the above-mentioned disease markers are relatively low, thus their detection results cannot be used as a diagnostic indicator of disease; (2) the early diagnosis rate of disease shall be positively correlative with the therapeutic effects. However, it is difficult for any of the aforesaid disease markers to meet such requirements for early diagnosis. Take cancer for example, the specificity of tumor differentiation is too high, the integrated sensitivity of tumor is relatively low, the samples sent to be detected are difficult to be repeatedly taken and the conditions to meet the preservation requirements for samples are too exacting, meanwhile, the cost is very high, thus under existing technology the spreading and use of the tumor markers available are hard to realize. The inherent defects of some traditional medical means such as biopsy, for example, incorrect material-extraction position, the inadequacy of sample materials for histocytes and human inexperience, etc., will all lead to misdiagnosis. Although other techniques such as imaging technique have been widely used for examination and diagnosis of diseases, there exists considerable limitation on the determination for disease degree. Consequently, it is very necessary to find out a maker for disease detection which is novel, sensitive and convenient to use and can also overcome the defects of existing markers as mentioned above.
MicroRNAs are defined as a kind of non-coding single-stranded small RNA moleculars of approximately from 19 to 23 nucleotides in length. They are highly conservative in evolution; and are closely related to many normal physiological activities of animals such as development process, tissue differentiation, cell apoptosis and energy metabolism; in addition, bear close relation with the occurrence and development of many diseases. Recent studies show that the expression levels of several microRNAs in chronic lymphocytic leukemia and Burkitt lymphoma are on average down-regulated to various extents; and that by analyzing and comparing the expressions of microRNAs in tissues of human lung cancer and human breast cancer, the expression levels of several tissue specific microRNAs have changed relative to normal tissues. Some studies demonstrate that microRNAs affect the occurrence and development of cardio-cerebrovascular diseases such as myocardial hypertrophy, heart failure, atherosclerosis, and are closely relative to metabolic diseases such as Diabetes II. These experimental results indicate that there exists inevitable connection between the expression and specificity changes of microRNAs and the occurrence and development of diseases.
For the unimaginable important role microRNAs played in the regulation of expression after gene transcription, microRNAs have some associations with diseases. First of all, the changes of microRNAs may be the cause of diseases. This is because both the inhibitor and the promoter of diseases may be target sites for microRNAs. If the expression of microRNA itself is disturbed, e.g., the expression level of microRNA which is originally to inhibit disease promoters decreases or the expression level of microRNA which is to inhibit disease inhibitor increases, its end results will both lead to changes in the expression of downstream genes and the overall disorder of some pathways, further inducing the occurrence of diseases. Secondly, the changes of microRNAs may also result from diseases. This is because, when a kind of disease such as cancer occurs, it will lead to the loss of chromosome segments, gene mutation or rapid amplification of chromosome segments; moreover, if the microRNAs happen to locate in the changing segment, then their expression level will extremely significantly change. Therefore, in theory, microRNAs can be completely regarded as a kind of new disease markers, the specificity changes of which inevitably correlate with the occurrence and development of diseases. Meanwhile, microRNA can also be used as a potential drug target, and it may greatly alleviate the occurrence and development of diseases by inhibiting the up-regulated microRNAs and overexpressedly down-regulated microRNAs in the course of a disease.
The inventor has carried out the research in the relevant fields of using microRNAs as disease markers, for instance, choosing colonic carcinoma which ranks forth in the incidence of malignant tumor as the research object. The research suggests that, during the process of colon benign polyps developing into malignant tumor, some microRNAs exhibit specificity changes, thereby a more sensitive and accurate method for the early diagnosis of colonic carcinoma having been set up through detecting the specific changes in microRNAs. However, since the sampling for tissue specimen is not easy, the wide application of this method in clinics is limited.